An oil well is a hole bored through layers of rock formations to reach a level or bed of petroleum or gas. The desired petroleum or gas is often found at a depth as deep as 25,000 feet to 30,000 feet. After the initial bore hole is drilled with a drilling rig, a casing is run into the bore hole and cemented to the sides of the bore hole to keep the bore hole from collapsing.
If a casing is provided along the entire length of the borehole, the casing is perforated at the proper level to permit the top of the petroleum or gas to enter the casing for recovery. The casing may be run into the bore hole down to the hydrocarbon producing formation. This technique is referred to as open hole completion. The portion of the bore hole below the deposit is then unprotected from collapsing.
Almost all of the gas or oil wells drilled require some type of treatment to render the well productive. This often includes the pumping of acid; or acid and different sizes and grades of salt; or sand pumped under high pressure to fracture the formation in the oil or gas bearing layer. When the treatment is completed, some debris, formed by thge acid, sand, salt or other material, is left in the bore hole. This commonly leads to closing the hydrocarbon or gas producing formations to stop recovery.
Several techniques have been developed to remove debris from within a bore hole. A reverse unit may be employed which includes a rotary device above the oil or gas bore hole to turn a drill pipe or tubing. The drill pipe or tubing has a drill bit on the bottom end thereof and is run down into the bore hole to drill through the debris for cleaning or cleaning by drilling the well deeper. The reverse unit includes a pump on the surface at the bore hole for pumping fluid down hole to recover the debris and pump it to the surface. However, this technique is not always possible. Sometimes, cleaning or drilling circulation is impossible. In other instances, fluid may not be placed in gas wells as it will push the gas back into the formation and prevent little, if any, recovery of the gas.
To overcome this problem, several wire line clean-out tools have been developed. The tools are placed down hole on a wire line or cable suspended from the surface. The wire line tools basically operate on two principals, either hydraulic or hydrostatic. A hydraulic device is disclosed in U.S. Pat. No. 4,190,113 to Harrison issued Feb. 26, 1980. This type of device operates by alternatively evacuating and pressurizing a debris chamber with a pumping unit activated by the wire line. A one-way valve entering the debris chamber from the bore hole permits debris to flow into the debris container when the container chamber is evacuated. The debris is blocked from flowing out of the bore hole by the valve when the chamber is pressurized. The pumping assembly is operated until the debris container chamber is full of debris. The tool is then removed and cleaned for reuse.
Fluid pumped by the pumping assembly is discharged horizontally from ports in the device into the narrow annular space between the device and bore hole. This inhibits fluid motion downward in this annular space past these ports. In another device disclosed in this patent, a tubing string extends to the surface above the debris chamber. A kelly permits rotation of a notched collar below the chamber through the tubing string to break debris crust in the well bore. The presence of an empty tubing string in the well bore raises the potential for tubing collapse if the hydrostatic pressure in the well bore acting on the walls of the tubing string becomes too large.
The previously known hydraulic types of tools have several shortcomings. The vacuum within the chamber is limited and heavy or large debris will not be recovered. The pumping action also permits the tool to become submerged within the debris and possibly be incapable of recovery by the wire line. An extremely costly and time consuming fishing job is then required to get the tool from the well.
U.S. Pat. Nos. 3,406,757, 3,446,283 and 3,651,867, issued on Oct. 11, 1968, May 27, 1969 and Mar. 28, 1972, respectively describe hydrostatic tools. Each of these patents is issued to Baumstimler. In a hydrostatic tool, the tool is run down the bore hole with a sealed debris chamber at atmospheric pressure. The tool is set down on top of the debris in the well. A valve is then opened permitting the fluid in the bore hole to enter the debris chamber. With sufficient fluid in the bore hole, the hydrostatic head is much greater than the atmospheric pressure within the debris chamber and the inrush of fluid entrains debris into the debris chamber. The tool must then be lifted from the bore hole to remove the debris in the debris chamber.
The hydrostatic tool also suffers shortcomings. The hydrostatic head in the bore hole where the debris is located must be relatively high to permit satisfactory operation of the hydrostatic tool. It is quite expensive to add sufficient fluid to the bore hole to achieve this hydrostatic head if it is not provided naturally. When the well is returned to production, the fluid has to be recovered and disposed of at additional cost. While the hydrostatic tool is effective on large and heavy debris, there is little control of how much the debris containing chamber will contain. Prior known tools provide little control of fluid motion once the debris chamber is exposed to the bore hole pressures and the hydrostatic tool can easily become submerged within the debris and require a fishing operation for removal.
A need exists for a tool which may be employed as either a hydraulic or hydrostatic tool without major modifications to achieve the advantages of either tool operation in a particular application. A need also exists to develop a tool with a capacity to provide sufficient forces to lift the tool in either mode of operation from within the debris in the bore hole. U.S. Pat. No. 2,992,682 issued July 18, 1961 to Yates discloses a combination tool operable in both the hydrostatic and hydraulic mode. However, this tool is not readily transferrable from one mode of operation to the other and still retains the shortcoming of other known tools in failing to provide an effective technique for removing the tool from the bore hole when buried in debris.
In addition to the debris found in the bore hole, larger objects can also become an impediment to drilling and production. The object can be, for example, broken tubing, a logging tool, a sinker bar, drill collars or many other possibilities. These objects are frequently surrounded by debris, making it difficult to grasp the object with conventional tools and possibly embedding the object within the debris. The object may even be totally submerged in debris which further complicates the removal thereof.
One common source of such objects that need retrieval are either a production string or a work string which has broken along its length or become so wedged by debris in the bore hole that it cannot be removed by merely pulling the string to the surface.
A need therefore exists for a technique to effectively remove such objects from within the bore hole. If they remain in the bore hole, these objects can reduce or completely stop production of the well. Such a technique must both provide for release of the object from the debris surrounding it and provide for lifting of the object to the surface for disposal.
As noted previously, there are many different methods of treating an oil well in order to enhance recovery of oil and gas from a hydrocarbon producing formation. One of the most common methods is the pumping of different grades and stages of sand, salt or acid and the like under pressure into the bore hole so that the pressurized material passes through the perforations in the casing of the well bore and into the formation. This pressurized material fractures the formation to form a fracture zone or enlarges already existing fractures in the oil and/or gas producing formation. This fracturing treatment opens up the formation, creating cavities and void spaces in the formation near the perforations in the casing. The fractures enhance the flow of gas and oil from the fractures, through the perforations and into the well bore.
However, fine debris, emulsions or natural formations such as sugar sand can collect in the formation, perforations and the well bore. As long as there is continuous fluid flow within the well bore, these debris materials will commonly remain in suspension and cause no reduction in production. However, if fluid motion ceases, the debris material will settle out of the suspended state and can create a blockage in the formation, the perforations through the casing or even within the well bore itself. These blockages can lead to significant decreases in well production. It can readily be seen that a decrease in production leads to significant economic losses.
Even if blockage does not occur with the debris, the supended debris will accelerate pump failure. The debris will cause excessive wear of the pump. Removing the pump for replacement or repair is expensive in itself and, of course, the cost is increased by the loss in production during the repair or replacement down time required.
In the past, tools have been used to remove the debris from the formation and the well bore by setting a pack-off device above the perforations in the casing opening into the formation, or in an open hole if no casing is present. A swab device is then run down hole on a sand line from the surface. The swab device swabs the casing and "surges" or pulls the debris from the formation into the well bore.
The swab device and pack-off device must then be pulled from the well bore. The debris must then be removed from the well bore in yet another step by using a conventional tubing inserted in the well bore. This technique has not been found fully effective. One reason is the relatively limited force that can be exerted by the movement of the swab device to drive debris from the formation into the well bore. In addition, the technique clearly requires at least two insertions and removals of separate devices in the well bore, increasing the time necessary to complete the operation.
One of the major functions of the casing within the well bore is to protect the oil and/or gas producing zone from contamination with other underground fluid materials, including salt water, mud and fresh water. If a perforation or hole is formed or produced through the casing, for whatever reason, near a zone of contaminating fluid, the productivity of the well bore can be decreased or even destroyed. When such a perforation or hole is present, it must be patched or "squeezed", typically with cement.
State and federal regulations exist to insure that any repairs made to a hole in casing meets the necessary standards to insure the casing performs its function of protecting the productive zone. Obviously, the operating company producing the well has a significant economic interest in making a fast and effective repair.
In order to effectively patch an undesired hole in the casing, the cement must normally be pumped through the hole under pressure and into whatever cavity volume exists in the formation outside the casing into which the hole opens. The cavity and hole in the casing must be filled to the extent necessary so that entrance of contaminating fluids will not occur from the cavity into the bore hole and well bore fluids will not pass through the hole into the cavity. The concrete will have a particular curing agent added to the cement slurry mix. If the cement sets before a complete "squeeze" is accomplished, then the cavity and hole must be resqueezed, if possible, to form a complete repair.
In many instances, debris will be present in the cavity, hole or immediate area that will reduce the flow of the cement into the hole and cavity beyond. Since the setting time of the cement is predetermined by the setting agent used, a reduced rate of cement flow caused by debris may inhibit or prevent a successful squeeze job.
Therefore, it is desirable to remove any debris in the area of the repair prior to a squeeze sealing up the hole and cavity beyond the cement. In the past, no tool or technique has been developed that adequately performed this clean out function prior to a squeeze.
Therefore, a need exists for a tool and method of use which can be employed to effectively surge and clean debris from a well bore, any perforations through the casing of the well bore and the formation beyond the perforations. In addition, a need exists for a tool and method for cleaning a well bore, a hole through the casing of the well bore and the cavity in the formation beyond to permit more effective squeezing of the hole.